diff --git a/tests/unittests.c b/tests/unittests.c
index cc4a3c1a..d804e550 100644
--- a/tests/unittests.c
+++ b/tests/unittests.c
@@ -90,7 +90,7 @@ int unit_tests(void *_unused) {
     }
 
     if (opt_ulong != 42) {
-        printk("Integer parameter opt_ulong != 42: %d\n", opt_ulong);
+        printk("Integer parameter opt_ulong != 42: %lu\n", opt_ulong);
         BUG();
     }
     else {